Sulfide glasses based on gallium sulfide and/or germanium sulfide have been modified to improve their properties with either alkali metal sulfides or rare earth sulfides. These two families of sulfide glasses have opposite thermal properties. The sulfide glasses modified with alkali metal sulfides have glass transition temperature (Tg) of less than about 300.degree. C. and glass stability, measured as the difference between Tg and crystallization temperature (T.sub.x), of about 60.degree.-130.degree. C. The sulfide glasses modified with alkali metal sulfides are also hygroscopic. The sulfide glasses modified with rare earth sulfides have Tg in excess of about 550.degree. C. but glass stability of only about 50.degree. to 130.degree. C. The low glass stability of the sulfide glasses modified with rare earth sulfides reduces their glass-forming ability. Furthermore, the two families of the sulfide glasses transmit light but only up to about 9 microns.
A sulfide glass is needed that has improved physical and optical properties.